The following demonstrates how to trigger email notifications by calling a remote messaging enpdoint using RestTemplate and JSON serialization.

Service Method

import com.alibaba.fastjson.JSON;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.HashMap;
import java.util.Map;

@Component
public class TaskNotifier {

    @Value("${notify.mail.endpoint}")
    private String mailApi;

    @Value("${notify.mail.sender}")
    private String senderAddress;

    private final HttpClientService httpClient;

    public TaskNotifier(HttpClientService httpClient) {
        this.httpClient = httpClient;
    }

    public void notifyTaskStopped(ScheduleTaskVO taskInfo) {
        Map<String, Object> payload = new HashMap<>(8);

        String timestamp = LocalDateTime.now()
                                .format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));

        payload.put("subject", "Scheduled Task Alert");
        payload.put("from", senderAddress);
        payload.put("to", taskInfo.getTargetEmail());
        payload.put("html", false);
        payload.put("content", String.format(
            "Hello, the scheduled task [%s] was automatically stopped at %s. Please investigate.",
            taskInfo.getName(), timestamp
        ));

        String jsonBody = "[" + JSON.toJSONString(payload) + "]";
        ApiResponse<String> result = httpClient.post(mailApi, jsonBody);

        if (result != null && "200".equals(result.getCode())) {
            JSONArray successList = JSON.parseObject(result.getData()).getJSONArray("successIds");
            if (successList.isEmpty()) {
                log.warn("Email delivery failed for task: {}", taskInfo.getName());
            }
        }
    }
}

Configuration

notify:
  mail:
    endpoint: ${api-gateway}/notify/email
    sender: alert@company.com

Response Model

import lombok.Data;
import java.io.Serializable;

@Data
public class ApiResponse<T> implements Serializable {
    private String code;
    private String message;
    private T data;

    public static <T> ApiResponse<T> success(T body) {
        ApiResponse<T> res = new ApiResponse<>();
        res.setCode("200");
        res.setMessage("OK");
        res.setData(body);
        return res;
    }

    public static <T> ApiResponse<T> error(String msg) {
        ApiResponse<T> res = new ApiResponse<>();
        res.setCode("500");
        res.setMessage(msg);
        return res;
    }
}

HTTP Client Utility

import org.springframework.http.*;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

@Service
public class HttpClientService {

    private final RestTemplate restTemplate;

    public HttpClientService(RestTemplate restTemplate) {
        this.restTemplate = restTemplate;
    }

    public ApiResponse<String> post(String url, String json) {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);

        HttpEntity<String> request = new HttpEntity<>(json, headers);
        ResponseEntity<String> response = restTemplate.exchange(
            url, HttpMethod.POST, request, String.class
        );

        if (response.getStatusCode().is2xxSuccessful()) {
            return ApiResponse.success(response.getBody());
        }
        return ApiResponse.error(response.getBody());
    }
}

HTML Table Email Example

StringBuilder html = new StringBuilder();
html.append("<html><head><meta charset='UTF-8'><style>")
    .append("table {border-collapse: collapse; width: 100%;}")
    .append("td, th {border: 1px solid #ddd; padding: 8px;}")
    .append("th {background-color: #f4f4f4;}</style></head><body>")
    .append("<p>Hello,</p><p>Material replenishment details:</p>| Req No | Code | Model | Qty |
|---|---|---|---|
| ").append(vo.getRequestNo()).append(" | ").append(vo.getCode()).append(" | ").append(vo.getModel()).append(" | ").append(vo.getQuantity()).append(" |</body></html>");

Map<String, Object> mail = new HashMap<>();
mail.put("subject", "Material Purchase Notification");
mail.put("from", senderAddress);
mail.put("to", recipient);
mail.put("html", true);
mail.put("content", html.toString());

httpClient.post(mailApi, "[" + JSON.toJSONString(mail) + "]");